'''
ITP-1_10-A
 ?????¢
?????? P1(x1, y1), P2(x2, y2) ????????¢????±???????????????°????????????????????????
???Input
x1, y1, x2, y2 ????????°???????????????????????§?????????????????????
???Output
P1??¨P2????????¢????????°??§?????????????????????????????????0.0001??\????????????????????£????????????????????¨????????????
'''
# # import
# import numpy
# 
# # inputData
# Data = input().split()
# x1 = int(Data[0])
# y1 = int(Data[1])
# x2 = int(Data[2])
# y2 = int(Data[3])
# 
# P1 = numpy.array([x1, y1])
# P2 = numpy.array([x2, y2])
# print(numpy.linalg.norm(P2 - P1))

import math

def get_distance(x1, y1, x2, y2):
    d = math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2)
    return d

if __name__ == '__main__':
    # inputData
    Data = input().split()
    x1 = float(Data[0])
    y1 = float(Data[1])
    x2 = float(Data[2])
    y2 = float(Data[3])

    d = get_distance(x1, y1, x2, y2)
    print(d) '''
ITP-1_10-A
 ?????¢
?????? P1(x1, y1), P2(x2, y2) ????????¢????±???????????????°????????????????????????
???Input
x1, y1, x2, y2 ????????°???????????????????????§?????????????????????
???Output
P1??¨P2????????¢????????°??§?????????????????????????????????0.0001??\????????????????????£????????????????????¨????????????
''' import math math def get_distance(x1, y1, x2, y2):
    d = math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2)
    return d get_distance d = math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2) d math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2) math.sqrt math sqrt (x2 - x1) ** 2 + (y2 - y1) ** 2 (x2 - x1) ** 2 x2 - x1 x2 x1 2 (y2 - y1) ** 2 y2 - y1 y2 y1 2 return d d x1 x1 y1 y1 x2 x2 y2 y2 if __name__ == '__main__':
    # inputData
    Data = input().split()
    x1 = float(Data[0])
    y1 = float(Data[1])
    x2 = float(Data[2])
    y2 = float(Data[3])

    d = get_distance(x1, y1, x2, y2)
    print(d) __name__ == '__main__' __name__ '__main__' Data = input().split() Data input().split() ().split () input split x1 = float(Data[0]) x1 float(Data[0]) float Data[0] Data 0 y1 = float(Data[1]) y1 float(Data[1]) float Data[1] Data 1 x2 = float(Data[2]) x2 float(Data[2]) float Data[2] Data 2 y2 = float(Data[3]) y2 float(Data[3]) float Data[3] Data 3 d = get_distance(x1, y1, x2, y2) d get_distance(x1, y1, x2, y2) get_distance x1 y1 x2 y2 print(d) print d x1 = float(Data[0]) float(Data[0]) x1 y1 = float(Data[1]) float(Data[1]) y1 d = get_distance(x1, y1, x2, y2) get_distance(x1, y1, x2, y2) d y2 = float(Data[3]) float(Data[3]) y2 x2 = float(Data[2]) float(Data[2]) x2 def get_distance(x1, y1, x2, y2):
    d = math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2)
    return d def get_distance(x1, y1, x2, y2):
    d = math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2)
    return d get_distance Data = input().split() input().split() Data
'''
ITP-1_10-A
 ?????¢
?????? P1(x1, y1), P2(x2, y2) ????????¢????±???????????????°????????????????????????
???Input
x1, y1, x2, y2 ????????°???????????????????????§?????????????????????
???Output
P1??¨P2????????¢????????°??§?????????????????????????????????0.0001??\????????????????????£????????????????????¨????????????
'''
# # import
# import numpy
# 
# # inputData
# Data = input().split()
# x1 = int(Data[0])
# y1 = int(Data[1])
# x2 = int(Data[2])
# y2 = int(Data[3])
# 
# P1 = numpy.array([x1, y1])
# P2 = numpy.array([x2, y2])
# print(numpy.linalg.norm(P2 - P1))

import math

def get_distance(x1, y1, x2, y2):
    d = math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2)
    return d

if __name__ == '__main__':
    # inputData
    Data = input().split()
    x1 = float(Data[0])
    y1 = float(Data[1])
    x2 = float(Data[2])
    y2 = float(Data[3])

    d = get_distance(x1, y1, x2, y2)
    print(d)